The National Cancer Institute has a need for development, standardization, and validation of assays that can quickly and cheaply determine or predict organ-specific toxicities of potential cancer therapeutic agents. The objective of the proposed project is to develop an in vitro liver cell assay to determine or predict potential dose-limiting hepatocellular injury and injury to the biliary tract by anticancer agents in humans. The research will focus on the development, verification, and validation of multicell systems that can meet that objective, in particular precision-cut liver slices and co-cultures of hepatocytes and biliary epithelial cells. The assay to be developed will be able to (1) discriminate the types of injury that can be produced in liver by anticancer agents, (2) discriminate differences in analogue sensitivity, (3) discriminate interspecies differences in sensitivity, and (4) identify indicators of diagnostic value in serum for identifying specific types of liver injury in humans. The research will evaluate known clinical diagnostics for their utility, sensitivity, and fidelity in detecting and quantifying the types of liver injury produced by anticancer agents in the assay and will search for novel indicators, using proteomic techniques in the R21 phase, that may be superior for identifying target cell injury and mechanisms in the assay and be clinically relevant and valuable. Reference compounds used to develop and validate the assay will be primarily anticancer agents with specific, well-defined, representative toxicities in animals and/or humans. The R33 phase will focus on developing the full capabilities of this assay as an important and critical part of the in vitro toxicity test battery needed by the NCI to screen for target organ toxicities and to aid in predicting safe dose levels and regimens for clinical trials.